There are different stages: childhood, adolescence, adulthood and old age.
First stage of life. Since you ar born until about 12 years old. Many changes take place. Babies do not have teeth, they do not know how to walk or talk. At this stage the milk teeth appear, which become definitive when they are 6 years old.
They learn many things about the world around them.
Between 12 and 16 years old. Your body and your mind change and prepare for adulthood. Boys and girls have different changes. In boys, their facial hair grows and their voice get deeper. The girls develop the breast and its shape changes.
Adolescents are becoming more independent and making their own decisions.
When you are an adult your body is fully developed. Adults stop growing and their changes are slower. In this stage people are ready to take responsibility. They work, take care of children and are an active part of society.
It is the last stage. Our body is weaker. Our skin has wrinkles and our hair is gray. People have more knowledge, experience and memory. We can learn a lot from people at this stage.